feat: new note creation — unsaved/in-memory state before first save (#112)

* feat: add pendingSave status indicator for new note creation

Track disk write state during note creation with a pulsing green dot
on tab and breadcrumb bar. The pending state resolves to 'new' once
the file is written to disk, giving users clear feedback during the
async save.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add tests for pendingSave status lifecycle

Cover resolveNoteStatus priority, createAndPersist callbacks,
TabBar pulsing dot indicator, and BreadcrumbBar "Saving…" text.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add design frames for new note creation pending save state

Two frames in design/new-note-creation.pen:
- Pending save: pulsing green dot, italic title
- Saved: static green dot, normal title

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* design: add new-note-creation frames (pending save + after first save)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/App.css

@@ -52,3 +52,12 @@
   from { transform: rotate(0deg); }
   to { transform: rotate(360deg); }
 }
+
+@keyframes tab-status-pulse {
+  0%, 100% { opacity: 1; }
+  50% { opacity: 0.3; }
+}
+
+.tab-status-pulse {
+  animation: tab-status-pulse 1.2s ease-in-out infinite;
+}